Added a snippet for ALTER TABLE...ADD COLUMN...AFTER ...

This does an ALTER TABLE dbo.table ADD COLUMN Id INT NOT NULL AFTER Column.
This needs to be invoked using "alteradd". The resultant SQL has been tested
to work in MySQL.
Added Perl mode support to YAS.

The Perl mode, at the moment, supports new packages, the "new" method, foreach
and functions. Will need a little more functionality.